The present invention relates to imaging spectrometers and, more particularly, to compact, multi-channel and/or multi-spectrum imaging concentric spectrometers.
A spectrometer is an instrument that separates radiation, such as light, into a spectrum of energy bands (wavelengths) and indicates the relative intensity of each band. In the case of visible light, a spectrometer typically separates the light into a spectrum that ranges from violet (short wavelength) light to red (long wavelength) light.
Analyzing a spectrum of electromagnetic energy that is reflected from, or emitted by, an object can assist in identifying the chemical composition or physical properties of the object. For example, spectrometers are used in astronomy to analyze the chemical composition of stars. In another example (“Raman laser spectroscopy”), an object is illuminated by a laser. The laser light excites atoms of the object, and these atoms emit light of a wavelength, or several wavelengths, different than the laser light. Comparing the wavelength of the laser light with the wavelength(s) of the emitted light can assist in identifying the chemical composition of the object. Raman and other laser spectroscopy techniques are used to analyze minerals and geological samples, semiconductor wafers, process manufacturing samples and chemicals, such as suspected biological or chemical warfare agents. In another example of spectral analysis, scanning a scene, such as a scene viewed from a reconnaissance aircraft or a satellite, with a spectrometer can be used to detect features of interest, such as freshly disturbed soil. Such an analysis can be useful in detecting freshly planted crops or recently laid landmines, for example. Products based on optical wavelength separation capabilities (such as multiplexers and de-multiplexers) can also be used in fiber optic telecommunication systems for optical wavelength switching to separate wavelength-division multiplexed (WDM) channels carried over a single optical fiber.
Conventional spectrometers used for Raman analysis are relatively large and heavy laboratory-based instruments, primarily due to the large optical focal lengths inherent in the designs of high resolution instruments. In addition, conventional spectrometers can produce spectra of fairly limited ranges of wavelengths at higher reciprocal dispersions.